Everybody seems to agree basically that :

• there are a form of unreusable questions which are less interesting and sometimes just poor,
• these come in great numbers,
• incentives for all questions being equal make them be part of the system

Core idea: High Reusability Potential (HRP) question status

Rather than negatively offsetting unreusable questions, I suggest quite the opposite (to hopefully achieve the same segregation): positively offsetting reusable questions.
Instead of focusing on what are bad questions and how to hide them, we should try to discriminate good questions and display them more prominently. So I propose a different status, with at least an indicator on the questions' page.

Then of course, we should give more visibility to HRP questions, such as

• creating a short-hand search filter for them, so that you may "limit the number of [visible] questions to a sane amount"
• pointing to them with duplicates and generally use them more as references,
• having search engines reference them more (if this is possible)
• enable the search filter by default, suggest to remove it if few hits
• [other suggestions welcome]

And let people lacking a hobby or desperate for internet points dig through non-reusable questions. Those will still be on-site, answered in maybe a good or a bad way, and have inherently bad or decent quality -- just not much reusability.

Identifying reusability

To be honest, reusable questions are rather easy to identify with metrics we already have (after some time): they attract upvotes†. With votes being open to all, and allowing everybody to upvote but discouraging downvotes sligthly, any question that is ever so slightly recurring in the community gets points.

So maybe set a threshold, such that HRP := (Score >= 10)?

Non-reusable questions

If we take the ghetto to mean place for poor or unreusable questions, this system defines (by contraposition) the "grey town" of questions -- which is either the ghetto or just a temporary place depending on whether at some point in the future, these questions will reach HRP status.

It is also less critical to get the limit between both categories exactly right if you don't remove the non-reusable questions.

The goal is of course not to remove grey-town questions (but still close off-topic or very poor questions the same way that we do today). Hence they will still "take up space" for the obscure or unforeseen case of re-applicability, and to them a chance to be promoted, but not for answerers who have little time to spare.

This might become some sort of a de-facto novice zone, but not on a separate site.

Incentives will make it work

To guarantee social promotion of questions, we need not encourage downvoting low quality content, but encourage upvoting quality content more, Because its probably easier to vote someone up than down (which is reinforced by the penalty incurred by downvoting).

What is critical to this system, is to let questions flow between both categories. I think the giving a visible HRP status on the question page, and Making the HRP threshold official would encourage people to upvote at least until this threshold is reached, whenever the question is well-asked, potentially reusable, and event if is not applicable to themselves (which in my experience, does not happen a lot today ^{[citation needed]}).

This makes the simple viewer less passive, gives him an opportunity of very quick and simple feedback even if he's not confident he is an export in the area. This makes him more of a promoter instead of a punisher of some form, giving him the "better" role. While it is often hard to pick why a question is poor, good questions are in my experience more easily identified (and often answered quickly).

Hopefully, this will also make people understand that curating their question will give it a higher visibility, and thus more chances of getting an answer.

Other new incentives, such as badges or privileges, may encourage people to dig through the grey town with more motivation than just out of boredom (or cravings for reputation). For example, new badge(s) for finding a question, and editing/promoting it until it reaches HRP, or a privileges per-tag to facilitate HRP, e.g. silver => votes count double but only towards HRP status, not question score or any other factor.

Good fit with respect to other opinions in this thread

This is an attempt to create two categories without resorting to pejorative vs meliorative vocabulary, as Peter Alfvin suggested.

HRP questions will fulfill goal 2 from Robert Harvey's answer, "To serve as a repository for useful programming knowledge.", while the grey town questions will fulfill goal 1, "To get people quick answers to their programming questions" -- but without letting "vague, obscure, under-specified questions from people who lack basic knowledge of their craft" drowning out valued posts.

This is basically a fancy way of implementing what Shog9 suggested using search filters, but with more incentives.

Potential downsides

• Potential points inflation -- but do we really care? Worst case, this is fixable by adjusting privilege prices thresholds
• Second wave of answers whenever a question slowly achieves HRP (is this really bad?)
• A risk of splitting the community two-ways? People living in the grey town vs people never removing the HRP filter. Though probably a lot of people will do both part-time and try to identify and fish out good questions, and everything should be done to encourage this open-minded behaviour.
• Might not solve the frustration of this question, which is that by the time reusable questions reach their HRP status, they might already be answered, and eager answerers will still have to dig through a heap of poor questions.

† with the exception of historical lock and similar questions, that gain upvotes from other factors such as entertainement

_{TL;DR: Just read the bold words, you lazy bum.}